The present invention was made while trying to develop a way of keeping food aboard an aircraft either hot or cold without the use of heating or refrigeration equipment aboard the aircraft.
At the present time, food is kept cool aboard an aircraft in one of two ways. One way involves placing the food within food carts and circulating chilled air through the carts. The second way involves storing the food (or beverage) within a cart and placing in the cart bags of dry ice or another refrigerated material.
Presently two methods are utilized for heating food aboard an aircraft. One involves bringing the food aboard the aircraft in a frozen state and then thawing the food out and heating it to a service temperature by the use of ovens aboard the aircraft. The other involves the use of electrically heated carts to either raise frozen food to service temperature or maintain heated food at service temperature.
U.S. Pat. No. 3,205,033, granted Sept. 7, 1965 to Blair E. Stentz and U.S. Pat. No. 3,042,384, granted July 3, 1962, to Henry J. Bauman, each discloses a food cart having two compartments. One of the compartments includes refrigeration apparatus and the other compartment includes an electrical heating element.
U.S. Pat. No. 4,397,159, granted Aug. 9, 1983 to Malcolm J. Dodd, discloses a service cart that is constructed to receive a pan of dry ice on an upper shelf of the cart, and which includes a small blower for circulating air over the coolant and throughout the service cart.
U.S. Pat. No. 4,026,351, granted May 31, 1977, to Bruno Biava, discloses a food transporting container for use by caterers and the like. The container includes removable internal end walls which are constructed to support food containing trays. The endwalls are hollow containers into which hot water is placed if it is desired to maintain the food heated and cold water is placed if it is desired to maintain the food cold.
A similar system but on a smaller scale is disclosed by U.S. Pat. No. 2,504,911, granted Apr. 18, 1950 to Alten E. Whitecar. This patent discloses providing a refrigerant container which is sized to be received within a lunch box, picnic basket, or the like. The refrigerant is frozen by placing the container in a conventional freezer and then the container is placed within the lunch box or the like.
U.S. Pat. No. 2,543,524, granted Feb. 27, 1951, to Gervasio Pinto De Oliveira discloses a food chest which is constructed to include an electric heating unit in its cover or a hollow container insert in which a heated substance is placed if it is desired to keep the food hot, or a cold substance is placed if it is desired to keep the food cold.
U.S. Pat. No. 4,579,170, granted Apr. 1, 1986, to Paul J. Moses and Mark G. Hofius discloses the use of a phase change material within a container for thermal energy storage applications. The primary disclosed use for the container is in solar energy systems.
U.S. Pat. No. 3,304,106, granted Dec. 8, 1981, to William R. Donnelly discloses a food container in the form of a serving vessel having a hollow bottom compartment into which a chemical compound or mixture is placed. Such compound or mixture absorbs and holds heat and is used for keeping food warm for an extended period of time.
A principal object of the present invention is to provide a structural wall for a food container or the like which has superior load carrying characteristics and internal cell spaces into which a phase changing material having a high heat of fusion is encapsulated. This wall may be termed a "thermo wall".